If I run the following command on my Fedora Core 4 box:
./configure --disable-debug ; make
It fails with the following error
alloca.c: In function 'xemacs_c_alloca':
alloca.c:155: error: address of register variable 'hp' requested
make[1]: *** [alloca.o] Error 1
make[1]: Leaving directory `/home/jmiller/cvs/xemacs/xemacs-21.5/src'
make: *** [src] Error 2
Running "./configure ; make" does compile.
Jeff